Ethyl acetate is useful in coating materials, as a solvent and as a starting material for a number of important industrial processes.
Conventionally, the formation of ethyl acetate was by esterification of acetic acid with ethanol, using an acidic catalyst, such as a mineral acid:
(1) CH.sub.3 OOH+C.sub.2 H.sub.5 OH.fwdarw.CH.sub.3 COOC.sub.2 H.sub.5 +H.sub.2 O; or by direct synthesis from acetaldehyde: PA1 (2) 2CH.sub.3 CHO.fwdarw.CH.sub.3 COOC.sub.2 H.sub.5.
However, since the esterification reaction (1) is an equilibrium reaction, it is necessary to continuously remove the water by-product in order to achieve high conversion efficiencies to ethyl acetate. Unfortunately, most known methods of water removal, such as distillation, are either energy intensive, expensive, or both. An additional drawback to reaction pathway (1) is that ethanol is a relatively expensive feedstock. Likewise, reaction (2) is unfavorable, since the starting material itself, acetaldehyde, is relatively expensive and quite unstable.
Accordingly, it would be optimum to be able to form ethyl acetate with relatively low value reactants and without the formation of water by-product to reduce the energy required to separate the water by-product from the ethyl acetate product. Formation of ethyl acetate by reacting acetic acid with ethylene solves both the stated problems. Ethylene is a low value olefinic gas produced in large quantities in many petroleum refineries, which if useful as a reactant in place of ethanol, would result in a direct cost savings with respect to the reactant feed. Also, since water would not be produced as a by-product, it would not be necessary to incur the expense of separating water from the desired product, ethyl acetate, such as by the energy intensive distillation process.
Several investigators have developed processes suitable for direct reaction of ethylene with acetic acid to form ethyl acetate. EP 0 031 252 A1 discloses proton-catalyzed reactions in which water is not a stoichiometric reactant catalyzed by metal cation-exchanged layered clays. Reaction of ethylene with acetic acid is disclosed. EP 0 073 141 A2 discloses a method for promoting the activity and/or extending the life of a cation-exchangeable layered clay catalyst, for example montmorillonite, bentonite or vermiculite, which catalysts are useful in the formation of esters from olefins and carboxylic acids. Reaction of ethylene with acetic acid to form ethyl acetate is disclosed. EP 0 538 826 A2 discloses reacting ethylene with acetic acid in the presence of a tungstophosphoric acid catalyst having a portion of the acidic protons of the tungstophosphoric acid replaced with cesium cations.
U.S. Pat. No. 4,365,084 and U.S. Pat. No. 4,448,983 both disclose preparation of alkyl carboxylates by reaction of an olefin with a carboxylic acid in the presence of particular zeolite catalysts. Reaction of ethylene with acetic acid over HZSM-12 is disclosed (Example 16). However, the reaction level is disclosed to be low.